Method of making roughened rubber product



Aug. 29, 1961 w. J. O'BRIEN ET Al. 2,997,746

METHOD OF MAKING ROUGHENED RUBBER PRODUCT Original Filed Aug. 1, 1955 2Sheets-Sheet 1 INVENTORS W JIM ATTORNEYS Aug. 29, 1961 w. J. O'BRIENETAL 2,997,746

METHOD OF MAKING ROUGHENED RUBBER PRODUCT Orizinal Filed Aug. 1, 1955 2Sheets-Sheet 2 mvEzy ToRs WWL l ATTORNEYS United Sttes Patent 6 Claims.(Cl. 18-58.7)

This invention relates to a method for the manufacture of elastomericand plastic articles having novel surface effects and to the resultingproducts. The demand for dipped articles of rubber and similar materialsfor ornamental or friction resistant surface characteristics hasresulted in the development of a number of processes designed to produceirregularities in the surface of the articles being treated. Forexample, dipped articles such as surgeons gloves have been treated withacids and other chemicals which have an etching effect on the surface ofthe articles producing pits and embossments having certaincharacteristics.

The methods heretofore used have not been fully satisfactory since theytend to have a weakening effect and substantially alter the internalstructure of the article particularly Where the material is of limitedthickness.

One method which has heretofore been used to some extent in producingsurface irregularities is by the use of salts which are sprinkled ordusted on to molds of uncoagulated latex producing local shrinkagethrough coagulation and resulting in a corrugated effect on the surface.Such methods leave much to be desired as they likewise result in asubstantial modification of the internal structure of the articles beingtreated.

It is a main object of the present invention to provide a novel methodof providing roughened surfaces of rubher or other materials Withoutweakening the internal structure or body of the article.

In general, articles of latex such as rubber gloves are made by dippinga suitable form of porcelain or other material into a bath of latexcontaining a vulcanizing agent whereafter the form is lifted out of thebath, dipped into a bath of a coagulant and then given a second coatingof latex. After this second ,dip in latex, followed by one or more dips,the coating is dried on the form, the edge at the wrist rolled to form abead and after heating for a period sufficient to cure the rubbermaterial, the glove is stripped off the form, dried in a tumbling barreland then turned right side out.

It has been found according to the present invention that a superiorform of friction resistant or roughened surface may be provided onelastomeric plastic articles, such as rubber gloves, etc. by thesuspension of a hydrophilic solid in a bath of an elastomeric or plasticsubstance wherein the solid is relatively insoluble followed byimmersion of a suitable mold or form into the bath and thereafterleaching or dissolving away the hydrophilic solid material from thesurfaces of the molded article.

Conveniently as a part of the ordinary process for the manufacture ofrubber articles, the articles while still on the mold after the primarydip are given an additional thin coating of rubber material in a bathcontaining suspended therein a quantity of hydrophilic solid particles.The hydrophilic solid being insoluble in the naphtha or otherhydrocarbon solvent employed for the rubber remains on the surface ofthe dipped article as discrete particles and the rubber articles arethen given the conventional curing treatment. Following coating of thearticles, they are dried, rolled and cured by heat- ICC ing, strippedfrom the form and thereafter subjected to a leaching or washing step insoapy water in accordance with conventional practice. This Washingtreatment however produces the additional function by dissolving thoseparticles of the hydrophilic solid which are adjacent the surfaces ofthe molded articles.

Referring to the drawings, a specific application of the invention hasbeen shown for illustrative purposes, and FIG. 1 embodies a rubber glovesurface modified according to the present invention.

FIG. 2 is a photoprint view illustrating a cross section taken throughthe thickness of the surface-modified elastomer.

FIG. 3 is a magnified view in photoprint showing a pitted or modifiedsurface produced according to the teachings of the present invention.

The newly developed process of producing surfacemodified rubber productspreferably consists of using natural or synthetic rubber or film formingplastic compounds in combination with a solvent for the rubber orrubber-like compounds with a water-soluble hydrophilic solid, which,after dipping, may be removed from the surface of the molded articleswith an aqueous solvent, such as the usual soapy solution employed inthe conventional washing of molded rubber articles. Crystalline solidmaterials such as common salt, sugar, sodium and potassium hydroxides,sodium carbonate and the like may be employed and have been found tohave the desired characteristics for purposes of the invention.

It will be appreciated that the proportions of ingredients may be variedwidely without departing from the spirit and scope of the invention. Thepreparations preferred 'for practicing the invention contemplateapproximately 6 to 12 parts by weight of the elastomeric or plasticmaterial, to parts by weight of a solvent for the elastomeric or plasticmaterial and 12 to 30 parts by weight of the hydrophilic solid material.

In one embodiment of the invention, the form for the glove or otherarticle is given the customary dip in a bath of latex, and this may befollowed by one or more subsequent dippings, depending upon thethickness desired in the finished article and the concentration ofsolids in the coating bath. In order to produce a roughened surface onthe finished article, the mold is then given a final dip in a bath ofpure gum rubber cement containing, in addition to the usual rubber andnaphtha or other solvent, small crystals of sugar suspended in therubber solution. The sugar crystals will not dissolve in the cementbecause the sugar is insoluble in the naphtha solvent for the rubber.

Following this final dip in the rubber solution containing the sugar orother suitable water-soluble solid material, the glove may be dried,rolled and finally cured. After the glove is stripped from the form asin the regular process it may be subjected to the customary leaching orWashing step in a bath, and during the Washing treatment the sugar isdissolved in the aqueous soapy medium, and Washed out of the pores ofthe overlying cement layer on the article.

The step of dissolving out the solid hydrophilic material from the outersurface of the article results in a multiplicity of small voidspreviously occupied by the hydrophilic solid particles.

It has been found that the voids or craters produced by this method oftreatment provide a very desirable roughened and slip-resistant finishin the completed articles. The surface irregularities produced in theforegoing manner are permanently fixed and substantially modify thesurface characteristics of the body as an integral part of the finalstructure. An important feature of the invention is that this treatmentproduces no weakening of the body as ordinarily results in the usualchemical toughening or etching processes.

The roughening or surface modification which results can be controlledwithin practical limits from an extremely light to very coarseroughening, by simply varying the amount of hydrophilic solid in theformula. Furthermore, additional modifications can be achieved byvarying the particle size of the salt or other hydrophilic solid so thatlarge voids can be made to occur at spaced points from one another onthe surface of the article. Also the use of very small particle-sizesolid material can produce relatively small voids in the surface whichcan be spaced at any suitable distance from each other to produce anydesired degree of toughening in the surface of the finished articles.

The following examples illustrate suitable coating compositions whichcan be employed in carrying out the principles of the invention. Theformulae set forth below are purely illustrative of typical compositionsemployed in the rubber and plastics industry, and are not to be deemedas limiting the scope of the invention.

EXAMPLE 1 Red neoprene cement-coating bath Lbs. Ozs.

Neoprene GN (polychoroprene White Factice 3 Stearic Acid. Zinc Oxide 3Light Magnesium O\1(le l Lithopone 4 \Vhlting (Chalk pigment). 7 OrangeColor 2 Red Color l 8 In formulating the rubber solution, the abovematerials are mixed together and dissolved in toluene in the proportionof approximately 3 lbs. of stock to each gallon of the solvent.Porcelain glove forms are dipped in this solution and then in a secondsolution similar to the first, but containing in addition 60 lbs. ofordinary granulated sugar. The forms were then dried and cured asindicated above to produce a roughened friction-resistant surfacesimilar to that shown in FIGS. 2 and 3 Paraplex 6-25 is a stable,permanently soft, thermoplastic, high molecular weight plasticizer forpolyvinyl chloride, which is manufactured by Rohm & Haas ofPhiladelphia, Pennsylvania. It is an alkyd-type polymeric polyesterresin based on a polybasic acid esterified with a polyhydric alcohol.

The solid materials were mixed together and incoporated into an organicsolvent in the proportion of approximately of a lb. of stock to onegallon of the solvent. Porcelain glove forms were then dipped into theresulting bath until the desired base thickness was built up on theforms, and thereafter the forms were given a single dip in a second bathcontaining the same composition, but in addition 75 lbs. of crystallinesalt. After drying and curing in the usual manner, the salt was removedfrom the surface pores by leaching with an aqueous soap solution.

A very thin film of gum rubber covers the salt crystals, and theinherent permeability of this thin film permits the water to have accessto the crystals. Initially the salt crystals absorb water, swell andtend to burst through the thin rubber film during the washing process.This produces a highly roughened surface.

Although substantially any solid hydrophilic substance may be employedwithout departing from the scope of the invention, hydrophiliccrystalline materials are preferred due to their availability and highsolubility characteristcs in aqueous soluton. By crystalline material ismeant a solidified chemical substance bounded by plain surfaces, usuallysymmetrical, and having the property of being rapidly soluble in aqueoussolution so that they are substantially removed from the surface of theelastomeric article, leaving surface voids and cavities. These surfacecavities or cellular formations have approximately the configuration ofthe crystalline particles previously situated in the cavities.

As used herein the term form is intended to include both matrix andpatrix forms or molds.

The solvent for the elastomeric material in the coating compositionwhich contains the hydrophilic solids must be water-immiscible so as tomaintain the integrity of the suspended solid matter until the coatinghas been finally cured on the surfaces of the article being treated.

This application is a continuation of applicants c0- pending applicationSerial No. 525,617, filed August 1, 1955 (now abandoned).

It will be appreciated that although specific embodiments of theinvention have been shown and described herein, the methods andcompositions may be widely varied without departing from the spirit orthe scope of the invention.

We claim:

1. The method of producing irregular surface characteristics on awater-impervious elastomeric article which comprises applying to saidarticle a permeable coating of an elastomeric composition, saidcomposition containing an elastomeric material, in a water-immiscibleorganic solvent having solid water soluble particles of hydrophilicmaterial suspended therein, curing the coating to eliminate the solventand solidify the composition, and then washing the elastomeric articlein an aqueous medium to dissolve the hydrophillic solid particles andproduce voids in the surface of the article.

2. The method of producing voids and irregular surface characteristicson a water-impervious elastomeric article which comprises providing saidarticle with a thin permeable coating composition, said coatingcomposition consisting essentially of from approximately 6 to 12 partsby weight of an elastomeric material, 75 to parts by Weight of awater-immiscible solvent for the elastomeric material, and 12 to 30parts by weight of particles of water soluble hydrophilic solidmaterial, curing the coated article, and then washing the article withan aqueous medium to dissolve the solid hydrophilic material from thesurface of the article, leaving voids in place thereof.

3. The method of producing an elastomeric waterimpervious article havinga coarsely roughened surface comprising the steps of dipping a form intoan aqueous bath of an elastomeric material to form a relativelywaterimpervious base coating on the form, thereafter dipping the coatedform into a coating composition containing an elastomeric material in awater-immiscible solvent having water soluble hydrophilic crystallineparticles suspended therein to form a thin permeable coating over thewater-impervious base coating, drying the article to solidify thecoatings, and washing the article with an aqueous solution which firstcauses the crystalline material to swell, the enlargement of theparticles bursting through the outer surface of the rubbery material,and then dissolves the crystalline material, thereby producing aroughened surface on the article. 7

4. The method of producing a rubber article having a roughened surfacewhich comprises forming a relatively water-impervious base layer ofelas'tomeric material of substantial thickness and strength by dipping aform in a water-miscible bath of latex material, applying externally tothe water-impervious base layer a thin permeable coating containing anelastomeric material in a water-immiscible organic solvent having a highconcentration of suspended particles of water soluble hydrophiliccrystalline material therein, solidifying the outer coating, andtreating the surface of the article with an aqueous solution to dissolveand remove the exposed crystalline material, thereby producingirregularities in the surface.

5. The method of roughening the surface of a rubber article whichcomprises coating a form for the article with an elast-omeric material,drying the thin permeable coating and applying thereto a coating of anelastomeric material in a water-immiscible solvent containing particlesof water soluble hydrophilic crystalline material in suspension, dryingthe second coating to produce a relatively thin permeable layer with thecrystalline material embedded therein, and treating the article with anaqueous medium to swell and then dissolve the crystalline material andproduce voids in the surface thereof, the swelling of the crystallinematerial bursting the outer surface of the thin permeable layer toincrease the roughening elfect.

6. The method of roughening the surfaces of Waterimpervious rubberarticles which comprises providing said articles with a thin permeablesurface coating of a curable rubbery material in a water-immisciblesolvent, the coating containing therein suspended water solublehydrophilic solid particles, drying and curing the coating of rubbermaterial, and washing the surface of the article with an aqueous mediumto remove therefrom the hydrophilic solids, producing surfaceirregularities on the article.

References Cited in the file of this patent UNITED STATES PATENTS1,710,617 Haddon et al. Apr. 23, 1929 1,988,709 Barns Jan. 22, 19352,266,716 Robertson Dec. 16, 1941 2,353,877 Choll ar July 18, 19442,393,1298 De Laney Ian. 22, 1946 2,503,139 Fabregues Apr. 4, 19502,736,926 Johnson Mar. 6, 1956 2,834,056 Miller May 13, 1958 2,867,849Drew et al. Jan. 13, 1959 UNITED STATES PATENT. OFFICE CERTIFICATE OFCORRECTION Patent No. 2,997,746 August 29, 1961 William J. O'Brien eta1.

It is hereby certified that error appears in the above numbered pat- Ient requiring correction and that the said Letters Patent should read ascorrected below Column 4, line 11, for "soluton" read solution column 5,line l4, strike out "thin permeable" and insert the same before"coating", second occurrence, in line 15, same column.

Signed and sealed this 6th day of February 1962.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

1. THE METHOD OF PRODUCING IRREGULAR SURFACE CHARACTERISTICS ON AWATER-IMPERVIOUS ELASTOMERIC ARTICLE WHICH COMPRISES APPLYING TO SAIDARTICLE A PERMEABLE COATING OF AN ELASTOMERIC COMPOSITION, SAIDCOMPOSITION CONTAINING AN ELASTOMERIC MATERIAL, IN A WATER-IMMISCIBLEORGANIC SOLVENT HAVING SOLID WATER SOLUBLE PARTICLES OF HYDROPHILLICMATERIAL SUSPENDED THEREIN, CURING THE COATING TO ELIMINATE THE SOLVENTAND SOLIDIFY THE COMPOSITION, AND THEN WASHING THE ELASTOMERIC ARTICLEIN AN AQUEOUS MEDIUM TO DISSOLVE THE HYDROPHILLIC SOLID PARTICLES ANDPRODUCE VOIDS IN THE SURFACE OF THE ARTICLE.